I have done testing with the divider notch, and without the divider notch. It seems that with a spacer on some combinations the notch may work. I have also seen on the dyno where there was a dip in the torque and hp curve at an unusual rpm that did not make sense, and it was because of that slot. When a manifold without the slot was used, the dip on the graph went away. It all comes down to testing, and trying every conceivable combination to find what works and what does not. I also find that on my flow bench when flowing dual plane intake manifolds that the ports nearest that slot have a turbulence, and lose flow at higher flow ranges on the bench. I believe that is the cause of torque fluctuations on the dyno. Depth of the plenum is also a factor because the deeper the plenum is, the more space is available for the airflow to turn into the runners instead of bouncing off the floor and having to make a right turn to get into the ports. Ted Eaton has done extensive testing with spacers with and without slots, and he has a lot of good information available on his web site. I have helped/watched several of these tests, and can verify what he prints there to be true. Joe-JDC
